1. Field of the Invention:
This invention relates to a vinyl chloride/vinyl acetate/maleic/anhydride (VC/VA/MA) polymer powder coating composition.
2. Prior Art:
Powder coating compositions based on a polymer of VC/VA/MA are known in the art; however, the known powder coating compositions are deficient in several important properties. These deficiencies prevent the known powder coating compositions from producing commercially superior coated metal products requiring a minimum of time and treatment to manufacture.
One deficiency is the known powder coating compositions' adhesive properties. Adhesive properties which are inadequate to produce commercially acceptable products prevent the known powder coating compositions from being adhered directly to metal substrates. To increase the adhesion between metal substrates and the known powder coating compositions the metal substrates are treated prior to being coated, thus producing another process step during the manufacture of coated products.
Another deficiency is the known powder coating compositions' thermostability. The known powder coating compositions do not have sufficient thermostability to prevent the VC/VA/MA polymer from being degraded during fusion at temperatures above 155.degree. C. This deficiency results in fusion being performed at lower temperatures for longer periods of time which increases manufacturing time, thereby decreasing the potential maximum production output.
The powder coating composition of this invention, unexpectedly and non-obviously, possesses excellent adhesion to untreated metal substrates and superior thermostability thereby allowing fusion at temperatures above 155.degree. C.